Slag Management Toolset for Improvised Gasifier Performance

Research is active on the development of computational tools for slag management during carbon feedstock gasification. This invention is available for licensing and/or further collaborative research from the U.S. Department of Energy’s National Energy Technology Laboratory.

Description

Gasification that relies on carbon feedstocks can face challenges associated with impurities in the feedstock, in the form of mineral and metallic compounds. During gasification, these materials can oxidize and/or melt, forming particles that coalesce at high gasification temperatures to form liquid slags whose viscosity depends on overall chemistry, the gasification temperature, and the gasifier oxygen partial pressure. Liquid slags can also interact with the gasifier liner, which is needed to protect the metal gasification chamber during the gasification process. The slagcorrosion of the refractory liner increases with increasing temperature, so gasifier operators typically try to operate the gasifier at low versus high temperatures. As the gasification temperatures decreases, however, the viscosity of a slag increases—becoming so viscous it will not flow from the gasifier. This situation forces a gasifier operator to either increase the gasification temperature to lower slag viscosity so it will flow, or to shut down the gasifier so the slag can be physically removed from it. Both scenarios can cause damage to the refractory liner, shortening its service life. Knowledge of how to control slag viscosity properties is critical to improving and maintaining the on-line performance of a gasifier.

Currently carbon feedstock is purchased based on carbon content, with little attention paid to its impact on gasification operation or refractory service life. Gasifier operators lack the knowledge to accurately predict slag properties from a specific carbon feedstock, or how to manipulate/manage the feedstock during gasification in relation to controlling the ash chemistry through slag additives or blending of different carbon feedstocks.

This technology describes a slag management computational toolset that enables a user to determine the optimal temperature for gasification of a carbon feedstock based on the chemistry of impurities (or additives) in the carbon feedstock that form slag in the gasifier.

The slag management model works by determining the optimal temperature range for gasification using known slag chemistry, viscosity, and temperature/viscosity relationships. When the slag management toolset is used to control slag properties, it can increase feedstock flexibility and decrease gasifier maintenance costs; changes that can be used to increase gasifier availability and lower syngas production costs. Additionally, the database of the slag chemistry and viscosity information can be expanded by adding public or proprietary information, allowing slag viscosity predictions to be optimized to a specific user needs.

Benefits

· The slag management toolset represents a new and unique method to predict slag viscosity for optimal gasifier operation based on carbon feedstock ash and additive chemistry

· The toolset allows for improved predictions of molten slag properties without the need to study slag structure or using regression fitting analysis

· Preliminary testing of the existing slag model by an industrial gasifier user demonstrated the toolset to be superior to commercially available slag models

· The slag management toolset can be customized to a specific user needs based on their slag chemistry/viscosity relationships

· The slag management toolset allows users to know in advance of purchasing a coal how ash impurities in it will impact gasification temperature, allowing a gasifier operator to predict in advance necessary modifications of that coal for their gasification process, and thus knowthe true cost of using a carbon feedstock